My "do all" 12.5

[dentron]

Objective for this build was to build a well rounded multi-purpose carbine that runs well and handles well.

I have 2 10" uppers and while I like them, I wanted something with increased range that doesn't sacrifice on manuverability with a can on. The 12.5" barrel is widely regarded as the perfect balance between velocity and handling.

Weight was a big factor for this build. Both my 10's have quad rails and while not the heaviest (they are DDs), I wanted something lighter. My last "accuracy oriented" 12" upper had a Larue stealth 12" with an ALG EMR 10" rail. That thing was way heavier than I liked, so it got parted out. I didnt want a pencil barrel, so I opted for a medium weight tapered barrel (Ballistic Advantage), and used a BCM KMR (non-alpha) 10" rail. My buddy has a 16" with a KMR and I am amazed how light it is every time I pick it up.

Barrel:
Ballistic Advantage 14.0" Hanson barrel cut down to 12.5" by ADCO. I really like the Hanson profile, but BA doesnt offer a 12.5 in it. So when Weapon Outfitters did a special run of 14.0"s with .060" gas ports, I hopped on it. When Iboriginally measured the port using drill bits and a digital micrometer, I thought it was at .058" however after further investigating, I believe it was .0595" (#53 bit/reamer). Either way, I used a 1/16" reamer (.0625") to open the port up. After testing, I have a .0650" reamer on the way, more on this below.

Buffer:
I wanted to port this to run suppressed and unsuppressed with just a swap of the buffer. After testing, I will have to accept a little over gassing suppressed to have the low end function that I want.

Testing:
Original port (0.0580-0.0595) with LMT E-carrier
Suppressed cycled and locked back all the way up to A5H4 with .223 and 5.55 ammo.
Would not cycle .223 or 5.56 unsuppressed with A5H2.

*I tested with a standard FA carrier, but it would not pick up the next round. All following tests were done with the E cartier*

.0625" port:
Since it already ran suppressed with .223 and the heaviest buffer, now I just needed to get the low end performance I desire. I also borrowed a A5H0 buffer so I could get a better picture of how much if any I would need to open the port. (If it ran with the H0 unsuppressed I woulf most likely leave it)
Unsuppressed:
A5H4 would run but not lock on 5.56 and .223 spec ammo
A5H2 ran and locked with 5.56 but no lock on .223
A5H0 locked back on .223 ~50% of the time.

Now here is where I am. I am going to open the port to .0650". I have a reamer on order (its special order because it is in between #53 and #52). I was hesitant to open the port past what a Colt barrel is at. Barrels with a smaller port than milspec are few and far between, so why go larger when I could cut down any barrel and have the port opened that large? I though about this and the only reason I would need a port that small is for a dedicated suppressed build which I dont think I want right now, and I like the hanson profile so cutting down a colt or similar would not give me that.

The .0650 port will be as large as I will go. I have read that is what Centurion ports their 12.5s to and that it works well. I would like it to run .223 realiably with atleast an A5H0 unsuppressed.

Moral of the story: ammo pressure matters, A LOT. Were I building a dedicated suppressed rig, or only running 5.56, that would dictate a different decision on the port size. In perspective though, .0650 is still small. I have read that: BCM ports their 11.5s at .076, Sionics ports their RGP 11.5 at .070, and crane specs .071 for 10.5(or 10.3). So this port is still conservative and should be gassed nicely.

I will be doing a post with some high speed video of the action soon and put it with the videos I am currently waiting on from the photographer. These include 10.5" barrel with a .070" port and "standard" carrier, a 10.3" with .073" port and a E Carrier, a BCM 14.5 with a E Carrier all tesed on A5h2s A5h4s and standard H2 buffers. As well as a 16" rainier barrel with a kynshot hydraulic buffer (the photographers).

Scope: primary arms 1-8x
I would really like a Nighforce 1-4x for this in the future, but the 1-8x is pretty cool and will work for now. I know it is not a "hard use" optic, but i have a PA RDS that works well and for the price, it will do. Also i wanted to try out the extended magnification over the more common 1-4 and 1-6s. Its alright, but i will definitely get something more quality in the future. And if it does fail, thats what the bobro and mbuis are for.

Now for the build list:

Standard mil spec upper reciever
Bcm 10" kmr
Custom cut and ported BA hanson barrel
Silencerco mount for my specwar k
LMT ecarrier
BCM bolt
Magpul buis
Primary arms 1-8x scope
Bobro mount
Bcm goodies on rail
Surefire light with bcm keymod mount

Lower:
Mckay industries lower
Umbrella corp lpk
Battle arms pins
Larue MBT trigger (i prefer this to my geissele)
Vltor A5 receiver extension
Standard stock
Umbrella corp grip

The painted stock and camo grip are takeoffs from other builds and just what I had laying around. The upper reciever was actually painted the same kac taupe as well but I removed (most of) it.

Overall, I feel it meets the goals I had. It is decently light, but not an extreme LW build, and handles nicely. The 12.5 gives me more velocity than my 10s and the 1-8x scope fits the purpose as well.

[msnyder0609]

That's a great looking rifle. How do you like the 1-8?

[porks]

Good looking rig.

[dentron]

That's a great looking rifle. How do you like the 1-8?

Eye relief is good on 1x, but definite fish eye on 1x. This is more pronounced indoors, less of an issue outdoors. Eye box on 8x is not very forgiving. But for the price I cant really complain.

The reticle is very good, and on 1x works well as a red dot substitute. If the illumination is too high in relation to the brightness of where you are looking, it will bleed to other parts of the reticle. Its not a set brightness when it happens, its all about how bright the rest of the sight picture is.

Overall, I think it offers a good close range usability and the 8x gives it way more usability at range than a 4x and a bit more than 6x.

[dentron]

Good looking rig.

Thanks bro, i want to compare the scope to your 1-6 next time we shoot.

[jerrysimons]

Very cool. Nice job.

What chamber does the barrel have? Recoil spring?
Cold weather and fouling can be a big factor for function also. Fouling can be approximated by "limp wristing" the rifle but cold weather can have big influences on pressure.

Can you describe your machining process and set-up? I am going for a similar build but using DIY gas-block inserts. Thinking a 12.5" carbine with .065" port or 11.5" carbine barrel with .067" port is the ticket, using the same overall configuration and span of operation desired.

[dentron]

Very cool. Nice job.

What chamber does the barrel have? Recoil spring?
Cold weather and fouling can be a big factor for function also. Fouling can be approximated by "limp wristing" the rifle but cold weather can have big influences on pressure.

Can you describe your machining process and set-up? I am going for a similar build but using DIY gas-block inserts. Thinking a 12.5" carbine with .065" port or 11.5" carbine barrel with .067" port is the ticket, using the same overall configuration and span of operation desired.

Thank you.
The barrel is chambered in 5.56
Recoil spring is Sprinco green
Every new years I go shooting in New Mexico and it is usually snowing. So I have experienced cold weather impacting function, another reason why I am ok with enlarging the port from what it is now. I do test without shouldering the rifle and a weak hold.

Opening the port was very simple. You need a good drilling setup, a reamer in the size you want, a set of numbered drill bits, and some cutting oil. Go SLOW and use a wooden dowel in the bore so you dont drill the other side. FYI i didnt even see the dowel move so check dept often. I was comfortable doing this by hand with the barrel in a vise. The reamer is so thin that you can see it bend if you arent lined up, and the existing gas port works as a guide.

But the insertable port is a little different. I have done those as well. I honestly wouldnt buy a specialty reamer or anything for that. Just thread a plate or the bottom plate of your drill press to 8-32, insert your socket head screw from the bottom and drill the size hole you want.

If you know the port size you want, and dont have a numbered drill bit set, i suggest looking into the BRT kit. It costs less than a drill set and is good kit. If you just want to diy cause you like doing stuff like that (me too) rock on.

[Clint]

Looks great Dentron!

What configuration(s) did you test with the standard FA carrier?

[jethroUSMC]

Eye relief is good on 1x, but definite fish eye on 1x. This is more pronounced indoors, less of an issue outdoors. Eye box on 8x is not very forgiving. But for the price I cant really complain.

The reticle is very good, and on 1x works well as a red dot substitute. If the illumination is too high in relation to the brightness of where you are looking, it will bleed to other parts of the reticle. Its not a set brightness when it happens, its all about how bright the rest of the sight picture is.

Overall, I think it offers a good close range usability and the 8x gives it way more usability at range than a 4x and a bit more than 6x.

IS your 1-8 the Platinum or standard offering from PA?

[dentron]

Looks great Dentron!

What configuration(s) did you test with the standard FA carrier?

Thank you! And thanks for your advice as well.

So far I have tested a standard FA carrier with original port (.058-.0595):

A5h2 suppressed ran
A5h2 unsuppressed did not run
A5h4 suppressed ran
A5h4 unsuppressed did not run

I did not test a standard FA carrier with the .0625 port or with a A5h0 buffer, i didnt have the H0 at the time of initial testing.

After testing the .0625 port / E carrier with the wider buffer range, I decided to go up to .0650" . I will test this port with both carriers to see how much difference there is at this size.

I have an A5h0, A5h2, A5h4 to test with. I think that will help me define the range I am working with, and if needed for fine tuning I will make an A5h1 or A5h3.